In a variety of industrial applications including agriculture, building construction, and road construction, by way of example, it is necessary or desirable to provide soil drainage to remove unwanted water. In agriculture, low spots in fields frequently are drained to prevent accumulation of excess moisture which would inhibit crop growth and yield. In construction, removal of pore water is frequently necessary to reduce unwanted settling of a structure due to gradual dewatering of saturated, compressible soils. See, e.g., U.S. Pat. No. 4,622,138.
In road construction, moisture immediately beneath the pavement surface causes distresses of varying types which may rapidly destroy the pavement. In flexible pavement systems, distresses may be caused by either water alone or in combination with temperature variations. Such distresses include potholes, loss of aggregates, raveling, weathering, alligator cracking, reflective cracking, shrinkage cracking, and heaving from repeated frost/thaw cycles and/or swelling soils. Rigid pavement system distresses include faulting, joint failure, pumping, various types of cracking, blow-up or buckling, surface spalling, steel corrosion, and heaving from frost/thaw and/or swelling soils. These distresses are discussed in more detail in U.S. Pat. No. 4,572,700.
A variety of drainage systems have been employed over the years in attempts to provide economical drainage systems to accomplish desired drainage objectives. Early drainage systems comprised filling trenches with sand and coarse aggregates in place of indigenous soils less permeable to water, such as clay. An improvement on these systems utilized synthetic textile fabrics (geotextiles) as a trench liner, filled with a coarse aggregate to support the fabric. Geotextiles prevent the aggregate from clogging with silt, thereby defining a drainage passageway. More recently, round perforated tubing has been used, typically placed in an aggregate filled trench, sometimes in combination with a geotextile covering the perforated conduit. See, e.g., U.S. Pat. No. 3,830,373; U.S. Pat. No. 4,182,591, and U.S. Pat. No. 4,572,700.
As discussed in detail in U.S. Pat. No. 4,572,700, many of these prior art drainage systems are relatively expensive to install due to being labor-intensive, and/or requiring removal and replacement of relatively large volumes of indigenous soil with preferred aggregate and/or sand backfill, processes involving extensive transportation of soil and backfill. Other products such as the drain strips shown in U.S. Pat. Nos. 4,639,165 and 4,572,700, intended to be less costly to install, are relatively fragile in their construction, and tend to not support the filter fabric adequately against soil pressures, particularly during backfilling.